As the FBI continued to investigate whether a projectile hit the Amtrak regional train that derailed outside Philadelphia on Tuesday, killing eight people and injuring more than 200, Congressman Paul Ryan once again rejected criticism of reductions in spending on the rail network which has mushroomed since the fatal accident.

Ryan, who chairs the House of Representatives ways and means committee and had already faced questions about Amtrak budget cuts this week, said on Sunday: “To suggest and insinuate that this tragedy could have been avoided or would have been avoided had Congress had some more spending, had Congress had a different budget, I think it’s the wrong suggestion and I think it should not be in this conversation.”

On Wednesday evening, barely 24 hours after the crash, the House appropriations committee voted on party lines to cut $250m from Amtrak funding . Democrats had attempted to boost such funding by $1bn, including $556m for the Northeast Corridor, the busy artery on which the Philadelphia crash occurred.

The stretch of track on which the crash occurred was not fitted with with the Advanced Civil Speed Enforcement System (ACSES), part of the Positive Train Control (PTC) system, which automatically enforces speed limits by slowing down or stopping trains that are going too fast or heading into danger zones.

On Saturday, the Federal Railroad Administration ordered Amtrak to improve safety by installing the system and improving warning signage for northbound trains on the Northeastern Corridor, which stretches from Washington DC to Boston.

On Wednesday, at a press conference at the scene of the trial, Robert Sumwalt of the National Transportation Safety Board said PTC would have prevented the accident.

“Based on what we know right now,” he said , “we feel that had such a system been installed on this section of track, this accident would not have occurred.”

Sumwalt was scheduled to appear on all five major political talkshows on Sunday. On ABC he repeated his point, saying: “We have seen countless accidents over the years that could have been prevented had Positive Train Control been installed.”

Sumwalt also called for inward-facing video cameras, which he said the NTSB had “called for for a long time”. He said such cameras on the train could have helped established what happened on Amtrak Regional Train 188.

That mystery continued to fascinate the media. On CNN on Sunday, asked about the possibility that the Amtrak train was hit by a projectile before it crashed, Sumwalt said FBI investigators would be at the site of the crash on Monday to continue “chasing this lead down”.

“We heard from the assistant conductor [of Amtrak Regional Train 188] and that’s what she believes she heard, was a conversation about that,” he said. “And we now see a mark on the windshield we want to look at. We’re going to look at everything.”

Sumwalt confirmed that an engineer on another train in the area had reported that his train had been “struck by something” on Tuesday, but he said there was “nothing at all from the Amtrak engineer to dispatch to say that his train had been struck”, despite what the assistant conductor said she heard.

The Amtrak train was travelling at more than 100mph in a 50mph zone when it left the tracks. On Sunday, Sumwalt said: “The only way that an operable train could accelerate would be if an engineer pushed the throttle forward and the event recorder does record throttle movement.”

He added that the Amtrak train’s engineer, Brandon Bostian, had been “fully co-operative” with the investigation. Bostian has said he remembers nothing of the crash.

The Associated Press, meanwhile, reported that Amtrak could pay out no more than $200m to victims and the families of victims of the crash, thanks to a law passed by Congress in 1997. Amtrak has never been liable for that maximum amount, the AP reported, though claims arising from the Philadelphia crash could be much higher.